1. Field of the Invention
The present invention relates to a field emission display, and more particularly, to a method for forming negative holes of the field emission display.
2. Description of the Related Art
Generally, screen-printing prints patterns designed on a screen of silk or other fine mesh, with certain areas coated with an impermeable substance. The paste is forced through the mesh onto the printing surface, leaving the coated area clean. Such a screen-printing is used in fabricating a low-voltage-driven flat panel display such as a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), and a vacuum fluorescent display (VFD).
One application of screen-printing is the fabrication of the FED, which will be described hereinafter.
The FED is designed to realize an image by emitting electrons from an emitter by generating a voltage difference between a cathode electrode and a gate electrode and letting the electrons strike corresponding red R, green G, and blue B phosphors formed on an anode electrode.
The emitter is formed on the cathode electrode exposed through negative holes of an insulating layer elevated to a predetermined height higher than the cathode electrode. Screen-printing is used to form the negative holes.
When forming the insulating layer on a substrate having the cathode electrode formed thereon, the insulating layer should be provided with negative holes for exposing the portion of the cathode electrode, because the emitter should be formed on a certain portion of the cathode electrode.
Accordingly, as shown in FIG. 1, a screen mask (not shown) provided with a photoresist layer corresponding to the negative holes NH is aligned with the substrate 122 on which the cathode electrode 120 is formed. Insulating paste is forced and squeezed through the screen mask onto the substrate 122 to print the insulating layer 124 on the substrate 122. At this point, on a portion of the substrate 122, which corresponds to the photoresist layer, the insulating paste is not printed to form negative holes NH.
Although such screen-printing is not costly and provides a simple process, it still has several problems.
When the paste is printed onto the substrate by a squeezing process through the screen mask, the paste may be blurred on the substrate due to the surface tension of the paste.
Accordingly, an edge portion 124a of the insulating layer 124 printed on the substrate 122 is blurred toward the inner side of the negative holes, making it difficult to form the negative hole NH having a diameter of less than 100 μm. In addition, this deteriorates the uniformity of the emitter patterns printed on a surface of the cathode electrode 120 exposed through the negative hole NH, thereby deteriorating the quality of the FED.
This phenomenon also occurs when the insulating layer 124 is printed after the emitters (not shown) are first printed. When the pattern size of the emitters is not uniform, the amount of electron coming from each emitter becomes different. This results in ununiform luminescence, thereby deteriorating the quality of the field emission display.